1. Field of the Invention
The present invention relates to a lithium secondary battery, and more particularly, to a method for treating electrode tabs of a crude cell for a lithium secondary battery, in which the capacity of the battery can be increased by increasing the length of electrode members without changing the predetermined specification of a battery package member, and stability of portions of electrode tabs where the tabs are welded to grids, respectively, can be enhanced by using insulation tap, and a crude cell for a lithium secondary battery manufactured according to the method and a lithium secondary battery employing the crude cell.
2. Description of the Related Art
In general, since portable electronic appliances such as a video camera, a portable phone, and a portable PC become lighter in weight and are designed to do various functions, various research and development concerning a battery used as an electric source of such electronic appliances have been performed. Such a battery is usually made to be rechargeable and can be used continuously.
Usually, among batteries, a nickel cadmium battery, nickel hydrogen battery, nickel zinc battery, lithium secondary battery, or the like is used as an electric power source of electronic appliances, and the lithium secondary battery of those batteries is generally used in consideration of its life time and capacity.
According to the type of electrolyte, the lithium secondary battery can be classified into a lithium metal battery and a lithium ion battery, which employ a liquid electrolyte, and a lithium polymer battery, which employs a polymer solid electrolyte. According to the type of polymer solid electrolyte, the lithium polymer battery can be classified into a full-solid type lithium polymer battery, which does not contain an organic electrolyte, and a lithium ion polymer battery, which employs a gel type electrolyte containing organic electrolyte liquid.
FIG. 1 is a perspective view schematically illustrating a structure of a conventional lithium secondary battery.
Referring to FIG. 1, the lithium secondary battery 10 comprises a crude cell 20 and a package member 40 for receiving the crude cell 20.
The crude cell 20 has a structure stacked with a plurality of unit cells 28 or bi-cells 27 according to a capacity of a battery. Here, as shown in FIG. 2A, each unit cell 28 is composed of an anode plate 22, a separator 24, and a cathode plate 26 in sequence, and as shown in FIG. 2B, each bi-cell 27 is composed of an anode plate 21, a separator 23, a cathode plate 25, a separator 23, and a cathode plate 25 in sequence.
As shown in FIG. 1, the crude cell 20 includes an anode tab 12 and a cathode tab 14. The anode tab 12 is formed by gathering anode grids 16 provided at respective anode plates and joining the anode grids 16 to an anode tab member 11 by welding. The cathode tab 14 is formed by gathering cathode grids 18 provided at respective cathode plates and joining the cathode grids 18 to a cathode tab member 13 by welding. The tab members 11 and 13 are provided with resin members 17 adhered to non-resin members 15 made of aluminum or nickel, respectively.
As shown in FIGS. 1 and 3, the package member 40 is provided with a receiving portion 32 into which the crude cell 20 is received and a sealing portion 34 which is hermetically sealed after the receiving portion 32 is filled with an electrolyte. The receiving portion 32 is composed of a first receiving portion 36 into which the anode and cathode plates are substantially received, and a second receiving portion 38 into which anode and cathode tabs 16 and 18 are received. The resin members 17 are interposed between the sealing portions 34, prevent the electrolyte (not shown) from leaking out, and prevent possible short circuit in the region of the tab members 11 and 13.
As shown in FIG. 3, in the structure of the conventional lithium secondary battery 10, when the width of the battery, and the thickness of the battery, i.e., the number of electrode plates are assumed to be the same as those of the other one, the capacity of the battery depends on the length of the battery, in particular, the length of electrode plates which contains an electrode material. Therefore, in order to increase the capacity of the battery, there is a method of increasing the length d3 of the first receiving portion 36 by decreasing the length d1 or length d2 of the whole length d of the battery, i.e., the length d1 of the second receiving portion 38 which is occupied by the anode/cathode tabs 12 and 14, or the length d2 of the sealing portion 34. That is to say, the length d3 of the first receiving portion 36 can be relatively increased as much as the decreased length of the length d1 of the second receiving portion 38 or the length d2 of the sealing portion 34. However, in the crude cell 20 of the conventional lithium secondary battery 10, since the minimum length of anode/cathode grids 16 and 18 and the minimum length of a weld portion 19 must be secured in the anode/cathode tabs 12 and 14, there is a limitation in which the second receiving portion 38 is to be considered as a dead space in the manufacturing process of the lithium secondary battery until now.
As shown in FIG. 3, there is a strong possibility that the package member 40 is damaged by the welded portion 19 to which the grids 16 and 18 and the tab members 11 and 13 are welded, or rough and sharp portions existing in the anode/cathode tabs 12 and 14. Therefore, in the conventional lithium secondary battery 10, there is a problem in which the package member 40 can be damaged by such a welded portion 19, or portions of the electrode tabs 12 and 14, this causes short-circuit to occur, and, therefore, the battery may malfunction.